Oakland police clashed with Occupy Oakland protesters on Saturday.

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Story highlights

NEW: Oakland City Hall reopens

NEW: Protesters vow to stand their ground at Occupy DC camp

Mass arrests in Oakland among largest in city history, police say

Arrests are reported in New York, Philadelphia and Tampa

CNN  — 

Oakland City Hall reopened Monday after municipal employees worked to clean up damage they said was caused over the weekend by Occupy protesters, about 400 of whom were arrested following clashes with police in the Northern California city.

Marvine White was one such worker, called in over the weekend to help scrub graffiti and vacuum floors, CNN affiliate KTVU reported.

“This is not protesting. This is something else. When you protest, you protest. This is madness here,” White said.

The mass arrests, described by police as the largest in city history, appear to have injected new life into the Occupy movement as protesters in a number of American and European cities took to the streets Sunday to express their solidarity with the Occupy Oakland group.

“The Occupy movement will respond, as we have always responded: With an overwhelming show of collective resistance,” Occupy Wall Street said in a statement posted on its website.

Windows broken, flags burned in Oakland City Hall

Occupy Oakland is part of a larger movement that began last year on New York’s Wall Street and quickly spread across the globe. While the protesters have highlighted a number of causes, the overarching theme remained the same: populist anger over what activists portray as an out-of-touch corporate, financial and political elite.

From Philadelphia to Des Moines, Iowa, there were reports of Occupy protesters taking to the streets in mostly non-violent demonstrations.

Twelve people were arrested in New York during an Occupy Wall Street protest that saw the group march from Gramercy Park to Tompkins Square Park, police said. Charges and details about the arrests were not immediately made available.

In Tampa, Florida, several protesters were arrested for blocking traffic, CNN affiliate Bay News 9 reported.

In Philadelphia, police reported several hundred protesters blocked traffic near City Hall and attempted to cut down a fence near an area park where Occupy protesters were recently evicted from camping out. Two protesters were arrested, according to CNN affiliate WPVI.

Overseas, Occupy protests were held outside U.S. consulates in Melbourne and Toronto, while statements of solidarity were issued by Occupy groups in Olso, Norway, and in Vancouver, British Columbia, according to Twitter and website posts late Sunday.

Much of the news stemming from the Occupy movement in recent weeks has focused on government efforts to relocate the protest groups, many of whom had taken up residence in city parks and plazas.

In Washington, D.C., the National Park Service gave Occupy protesters a deadline to end what it called “sleeping activity” at two longstanding camps established by demonstrators in the nation’s capital. U.S. Park Police began enforcing the ban Monday, with Occupy protesters at one site defiantly huddling under a large blue tarp that they dubbed the “tent of dreams.”

Park service to crack down on Occupy DC camps

Park police used a stun gun to apprehend one demonstrator, who tore down park service notices warning protesters of the Monday deadline.

But none of the weekend activities rose to the level of violence witnessed in Oakland, where protesters on Saturday clashed with police after they were prevented from taking over a long-vacant auditorium in the heart of downtown.

Protesters and police traded allegations over who was to blame for the violence that saw demonstrators throw rocks and bottles at police, who it turn fired bean bag rounds, tear gas and smoke grenades at the group.

Oakland Police Officer Johnna Watson described what transpired as “one of the largest mass arrests that we have seen in the city.” The charges ranged from failure to disperse to vandalism, Watson said.

The city of about 420,000, located across the bay from San Francisco, has a long and sometimes violent history of activism dating back to the mid-1960s with the founding of the militant Black Panther Party and later for its anti-war protests.

Oakland has been a flash point of the Occupy movement since October, when police used tear gas to break up demonstrators who refused to leave downtown. One demonstrator, an Iraq war veteran, suffered a skull fracture after being hit with a police projectile, according to a veteran’s group. Police said they acted after the crowd threw paint and other objects at officers.

In November, violence broke out again in Oakland when police shuttered an Occupy camp at an area park.

Twice, protesters have forced the shut down of the Port of Oakland.

But Saturday marked a new chapter in the Oakland Occupy movement when the group attempted to take over the long-vacant Henry Kaiser Convention Center to use as a hub.

The group said it was necessary, in part because “since November, the city of Oakland and its police force have made it impossible for us to meet, to serve food and to provide a place for people to stay.”

The effort turned violent when police turned the group back, alleging the protesters were damaging construction equipment and fences near the convention center.

By nightfall, the protesters stormed a YMCA and later broke into City Hall, police and city officials said. Protesters have decried the allegations, saying they entered the buildings through open doors.

But Mayor Jean Quan told reporters that police have video showing protesters using a crowbar, or something similar to it, to pry open an emergency door to enter City Hall.

Quan took reporters through City Hall on Sunday, pointing to walls where graffiti had already been painted over and other areas of garbage, vandalism and destruction that she said had been left by protesters.

The mayor said there were no firm estimates as to how much damage had been caused, noting that workers had already painted over some “obscene” graffiti and that clean-up efforts would continue.

Meanwhile, Occupy Oakland put out a call for financial aid to help some of those arrested make bail.

“Our bail funds have been dwindling significantly as a result of the police backlash against occupy Oakland in the last month. If you are able, please donate,” the group said.

CNN’s Karan Olson, Greg Morrison, Marina Landis and Maria P. White contributed to this report.